5,8-Disubstituted crown-naphthalonitriles as a platform for highly soluble naphthalocyanines

Abstract

The approach toward synthesis of 5,8-disubstituted naphthalonitriles as the universal platform for the range of novel functionalized highly soluble and nonaggregating naphthalocyanines was developed. The selective bromination of 15-crown-5-naphthalonitrile was described, that can pave way to wide application of transition-metal catalyzed cross-coupling reactions for the synthesis of functionalized naphthalonitriles and naphthalocyanines based on 6,7-dialkoxy-substituted precursors. Copper(II) complexes with heptynyl- and heptyl-substituted tetra-15-crown-5-naphthalocyaninates (2Cu and 3Cu) were synthesized from corresponding 5,8-disubstituted naphthalonitriles. It was shown that introduction of substituents into these positions efficiently suppresses aggregation of naphthalocyanines – the studied complexes were highly soluble in organic solvents and stayed in monomeric form in solutions up to 10−3 M according to UV–Vis and ESR studies. In contrast to previously described tetra-15-crown-5-naphthalocyanines 1M (M = Zn(II), Mg(II), 2H), complex 2Cu form cation-induced cofacial supramolecular dimer only in the presence of excess of potassium cations, while complex 3Cu didn't form supramolecular cofacial dimer. In addition the studied complexes demonstrate high photostability in comparison with Mg(II) and Zn(II) derivatives. Notably, introduction of heptynyl-substituents into 5,8-positions of naphthalocyanines did not lead to significant shift of the Q-band in UV–Vis spectrum, which was explained by quantum-chemical calculations using simplified TD-DFT approach, firstly applied herein to naphthalocyanine systems.